1. Field of the Invention
The present invention relates to a pneumatic bias tire for use on rough roads and more particularly to a pneumatic bias tire with a carcass having improved durability for use in a large wheel loader and the like.
2. Related Art Statement
Generally, a pneumatic bias tire for use on rough road, used for a large wheel loader and the like has a problem such that when running, cords in carcass plies may be repeatedly subjected to compression strain which ultimately results in cord breaking up (CBU) caused by fatigue thereof. Also, the carcass plies may be subjected to shearing strain producing fine cracks between the carcass plies which also ultimately results in burst of tire.
In order to solve the aforementioned problems, heretofore, it has been proposed to increase number of carcass plies to uniformly improve the rigidity of the whole carcass or to insert rubber sheets extending from one of beads to another bead between carcass plies to uniformly improve the rigidity of the whole carcass.
However, such a tire having improved carcass rigidity shows an effect sufficient to prevent the cord breaking up, but there have been raised other problems such that the weight of the tire is largely increased as well as the manufacturing cost is largely increased since the number of carcass plies or rubber sheets is necessarily increased as the condition of using of the tire became severe. Such a problem is particularly significant in a large tire having a carcass composed of not less than twelves carcass plies.